The emergence of Web services represents a shift from component-based architectures that have proved successful in the context of enterprise computing to service-oriented architectures that are more suited to the highly distributed Internet-based applications. This trend towards service-oriented computing necessitates the re-evaluation of software development methodologies that are used in the construction of distributed applications. With growing acceptance of service-oriented computing and increasing number of large-scale Web Services projects there is some evidence that practitioners involved in implementing these solutions are paying only limited attention to how such applications should be designed. Frequently, the design of Web Services applications is driven by performance and scalability considerations, rather than any sound software engineering principles. A comprehensive methodological framework is required to guide designers and developers of service-oriented applications through the various phases of software development life cycle with specific emphasis on producing stable, reusable and extendable services.

In this paper we discuss design of service-oriented applications from a software engineering perspective, and propose a software development framework for Web Services based on identification of elementary business function using business function decomposition and mapping these functions to service operations. We apply interface design principles adapted from object-oriented design as guidelines for the design of services.